Following Outlander episode 205, “Untimely Resurrection,” it was a big reveal that Black Jack Randall returned from the dead. This is the ultimate secret that Starz and co have kept from non-book readers this season. They chose this instead of Claire going back thought the stones and returning to Frank, which was spoiled in trailers leading up to the season premiere.
In the wake of the return of Black Jack, Starz released a new featurette with interviews with showrunner Ronald D. Moore, Caitriona Balfe, Sam Heughan, and Tobias Menzies. There is also some new footage from this season.